I also love the noise cancelling feature and find Airplane #4 most effective at reducing noise on my daily train commute. When flying I've used the adapter that allows you to plug into an aeroplane's entertainment system and the NC also works very well here (set at around #9 or #10).

An impedance adaptor would work to reduce hiss, but it'd disable NC functions. t seems that your only chance to have NC and lessen hiss is to solder a resistor in line with only the headphone wires, but that'd be very hard work.